This invention relates to a device for transferring control or drive signals or pulses between machine portions in mutual rotation relationship, particularly in a circular knitting machine. In order to transfer electric control pulses or signals between a stationary portion and rotating portion of a machine, e.g. between the stationary needle cylinder and rotary cam holding structure in a knitting machine, it has been proposed of using commutator and brush devices. The signals, which are effective to control elements of the machine such as solenoid valves of electro-pneumatic actuators for the needle selection slides, are transferred electrically by sliding contact between the commutator and its related brush.
These prior transfer or transmission devices operate substantially without problems with signals at relatively high voltage or current levels and at industrial range frequencies. However, they may give problems of space cluttering and weight where many components are to be controlled, one commutator and respective brush being generally required for each component to be controlled.
These devices are, above all, unsuitable for use with low level signals, e.g. on the order of some milliamperes and few volts, as are those employed for digital signal transmission in transferring control pulses for certain machine components. In this case, the sliding contact, whose resistance is highly variable, may introduce alterations in the typical electric parameters of the signals, which alterations may be deep ones with respect to the parameter involved and reflect in control errors. The very leads which conduct the signals may be a cause for mutual interference, especially with high frequency signals. Further, they may pick up noise interference which can induce an error in the signal itself.
Where the signal is to be also transferred with the machine at rest, then a different contact resistance occurs from that with the machine in operation, and this may lead to inaccuracies in the value of the signal transmitted in either cases.
Such problems are generally encountered not only with circular knitting machines but also with other machines including rotary portions, such as manufacturing machines in general, packaging machines of the rotating carousel type, machine tools having plural circularly distributed stations, and the like.